Can somebody explain how ohm loads work?
08-19-2008, 09:30 PM
#1
0 Watt CAFz'r
Thread Starter
Join Date: Jul 2008
Posts: 8
Can somebody explain how ohm loads work?
Why is it bad to run dif ohm loads from the amp to the sub. Say a 2 (amp) to a (4) sub. Or even a (2) to a (3) jl sub. What performance compromises should you expect from this? Say if you ran a lower amp ohm load to a higher ohm sub load. Does this mean less power will be delivered overall? If so can you compensate with more power to make up for the power lost. Im probably way out of my element here. Sorry for the really stupid questions. Im just trying to get a feel for what I should be buying etc.
Is there a good faq on the net that doesnt rely on technical terms to explain everything. I mean if you are starting out, it would be better to get a general idea for what everything does.
I do know that you have to match the amp to the sub RMS wise, but is there any other values that I should be worrying about aswell?
Thx for your time.
Chris
Is there a good faq on the net that doesnt rely on technical terms to explain everything. I mean if you are starting out, it would be better to get a general idea for what everything does.
I do know that you have to match the amp to the sub RMS wise, but is there any other values that I should be worrying about aswell?
Thx for your time.
Chris
08-19-2008, 10:05 PM
#2
50 Watt CAFz'r
Join Date: Aug 2008
Posts: 61
The load a sub (or any speaker for that matter) presents to an amplifier is called impedance (Z). Impedance is a complex thing, it's made up of alot of different components. There's mechanical losses (QMS), electrical losses (QES) as well as the direct current resistance (DCR) of the voice coil itself (because it is a simple inductor after all). You can manipulate the mechanical losses of a speaker to a certain extent depending on the enclosure you use, if you mass-load a sub (like in an isobaric configuration), but the other components that make up impedance are predetermined by the construction of the speaker and not really open to change.
That's the very basic technical end of it. I left out the formulas used to determine Z, as it's not really relevant here.
Now, how does this impedance thing apply to me and my amp. Well, if you have an 8 ohm sub on an amp rated at 1 ohm mono for example, the amp won't be making it's most power. But, the ability of the amplifier to control the sub will be very good. This is called damping factor, and can be directly correlated to the amount/capacity of transistors/FETs used to drive the speaker. A big amplifier with alot of output devices is going to have a better damping factor than an amp with fewer devices. You see, a sub will take the electrical energy an amplifier makes (voltage, current and frequency) and by energizing the coil (which becomes an electromagnet), it turns electrical energy into mechanical energy. A speaker gets AC voltage, and the frequency will vary depending on the tones, music played, etc. AC reverses it's current at the frequency (measured in forward/reverse cycles per second, or Hertz), therefore the speaker's voice coil reverses it's magnetic poles at that same frequency. This why a speaker seems to move in and out, rather than moving in just one direction only. But a speaker's cone has mass, it doesn't simply stop on a dime when the impulse from the amplifer stops, changes frequency, etc. When the amp is not giving an impluse, but the speaker still moves, it becomes an electric generator, making voltage and current. The amplifier must absorb this, and the more devices an amplifier has, the easier and quicker it can do it. When it absorbs this energy, the sub will stop almost dead in it's tracks. This is a passive form of control that has been used to stop electric motors known as braking. The more control a speaker is under, the more detailed and crisp it's output will be, and this is a measure of fidelity.
Confused yet? Good. That means you're reading this and trying to get a handle on it.
Now, back to loading. If you take that same 1 ohm-rated amplifier, and add 2 8-ohm subs, the load becomes 4 ohms. Doubling impedances give you 1/2 net load. The amplifer will make double current based on Ohm's Law, but it comes at a price. Damping factor will be cut in half, as the amp has to control 2 subs now instead of 1. Adding another 8 ohm sub will give you a load of 2.66 ohms, and adding another will give you a 2-ohm load. I leave out the math to calculate that, as it isn't relevant for basic theory of amp-speaker interaction. Every time you halve the impedance, you are forcing the amplifier to follow Ohm's Law and double it's current output to the speaker.
Current is the big problem for amplifiers. As all amplifiers are DC-AC inverters, they need to have a stable power supply to work well. The DC side will have a fixed power supply (I mean fixed tranformation, but variable output loading), with maximums for both voltage and current. As you load an amplifier down, you are asking it to make more current, but this current has to come from somewhere, namely your vehicle. And innefficient sub with a low impedance hooked up to a huge amplifer will mean big current draw.
But how does different impedance ratings of subs compare to each other? They don't, not in any way shape or form. A 1 ohm sub is not better or worse than an 8 ohm sub. Each sub has qualities that may be better suited to each system's individual needs. Find the sub that best suits your style of music (don't buy 8" subs if you like loud hip-hop) and your amplifier (don't buy a $1000 1ohm monster for a 50 watt amplifier).
That's the very basic technical end of it. I left out the formulas used to determine Z, as it's not really relevant here.
Now, how does this impedance thing apply to me and my amp. Well, if you have an 8 ohm sub on an amp rated at 1 ohm mono for example, the amp won't be making it's most power. But, the ability of the amplifier to control the sub will be very good. This is called damping factor, and can be directly correlated to the amount/capacity of transistors/FETs used to drive the speaker. A big amplifier with alot of output devices is going to have a better damping factor than an amp with fewer devices. You see, a sub will take the electrical energy an amplifier makes (voltage, current and frequency) and by energizing the coil (which becomes an electromagnet), it turns electrical energy into mechanical energy. A speaker gets AC voltage, and the frequency will vary depending on the tones, music played, etc. AC reverses it's current at the frequency (measured in forward/reverse cycles per second, or Hertz), therefore the speaker's voice coil reverses it's magnetic poles at that same frequency. This why a speaker seems to move in and out, rather than moving in just one direction only. But a speaker's cone has mass, it doesn't simply stop on a dime when the impulse from the amplifer stops, changes frequency, etc. When the amp is not giving an impluse, but the speaker still moves, it becomes an electric generator, making voltage and current. The amplifier must absorb this, and the more devices an amplifier has, the easier and quicker it can do it. When it absorbs this energy, the sub will stop almost dead in it's tracks. This is a passive form of control that has been used to stop electric motors known as braking. The more control a speaker is under, the more detailed and crisp it's output will be, and this is a measure of fidelity.
Confused yet? Good. That means you're reading this and trying to get a handle on it.
Now, back to loading. If you take that same 1 ohm-rated amplifier, and add 2 8-ohm subs, the load becomes 4 ohms. Doubling impedances give you 1/2 net load. The amplifer will make double current based on Ohm's Law, but it comes at a price. Damping factor will be cut in half, as the amp has to control 2 subs now instead of 1. Adding another 8 ohm sub will give you a load of 2.66 ohms, and adding another will give you a 2-ohm load. I leave out the math to calculate that, as it isn't relevant for basic theory of amp-speaker interaction. Every time you halve the impedance, you are forcing the amplifier to follow Ohm's Law and double it's current output to the speaker.
Current is the big problem for amplifiers. As all amplifiers are DC-AC inverters, they need to have a stable power supply to work well. The DC side will have a fixed power supply (I mean fixed tranformation, but variable output loading), with maximums for both voltage and current. As you load an amplifier down, you are asking it to make more current, but this current has to come from somewhere, namely your vehicle. And innefficient sub with a low impedance hooked up to a huge amplifer will mean big current draw.
But how does different impedance ratings of subs compare to each other? They don't, not in any way shape or form. A 1 ohm sub is not better or worse than an 8 ohm sub. Each sub has qualities that may be better suited to each system's individual needs. Find the sub that best suits your style of music (don't buy 8" subs if you like loud hip-hop) and your amplifier (don't buy a $1000 1ohm monster for a 50 watt amplifier).
Last edited by macguyver; 08-19-2008 at 10:10 PM.
08-20-2008, 05:34 PM
#3
0 Watt CAFz'r
Thread Starter
Join Date: Jul 2008
Posts: 8
The load a sub (or any speaker for that matter) presents to an amplifier is called impedance (Z). Impedance is a complex thing, it's made up of alot of different components. There's mechanical losses (QMS), electrical losses (QES) as well as the direct current resistance (DCR) of the voice coil itself (because it is a simple inductor after all).
You can manipulate the mechanical losses of a speaker to a certain extent depending on the enclosure you use, if you mass-load a sub (like in an isobaric configuration), but the other components that make up impedance are predetermined by the construction of the speaker and not really open to change.
That's the very basic technical end of it. I left out the formulas used to determine Z, as it's not really relevant here.
Now, how does this impedance thing apply to me and my amp. Well, if you have an 8 ohm sub on an amp rated at 1 ohm mono for example, the amp won't be making it's most power. But, the ability of the amplifier to control the sub will be very good. This is called damping factor, and can be directly correlated to the amount/capacity of transistors/FETs used to drive the speaker. A big amplifier with alot of output devices is going to have a better damping factor than an amp with fewer devices.
You see, a sub will take the electrical energy an amplifier makes (voltage, current and frequency) and by energizing the coil (which becomes an electromagnet), it turns electrical energy into mechanical energy. A speaker gets AC voltage, and the frequency will vary depending on the tones, music played, etc. AC reverses it's current at the frequency (measured in forward/reverse cycles per second, or Hertz), therefore the speaker's voice coil reverses it's magnetic poles at that same frequency. This why a speaker seems to move in and out, rather than moving in just one direction only. But a speaker's cone has mass, it doesn't simply stop on a dime when the impulse from the amplifer stops, changes frequency, etc. When the amp is not giving an impluse, but the speaker still moves, it becomes an electric generator, making voltage and current. The amplifier must absorb this, and the more devices an amplifier has, the easier and quicker it can do it. When it absorbs this energy, the sub will stop almost dead in it's tracks. This is a passive form of control that has been used to stop electric motors known as braking. The more control a speaker is under, the more detailed and crisp it's output will be, and this is a measure of fidelity.
Confused yet? Good. That means you're reading this and trying to get a handle on it.
Now, back to loading. If you take that same 1 ohm-rated amplifier, and add 2 8-ohm subs, the load becomes 4 ohms. Doubling impedances give you 1/2 net load. The amplifer will make double current based on Ohm's Law, but it comes at a price. Damping factor will be cut in half, as the amp has to control 2 subs now instead of 1.
Adding another 8 ohm sub will give you a load of 2.66 ohms, and adding another will give you a 2-ohm load. I leave out the math to calculate that, as it isn't relevant for basic theory of amp-speaker interaction. Every time you halve the impedance, you are forcing the amplifier to follow Ohm's Law and double it's current output to the speaker.
Current is the big problem for amplifiers. As all amplifiers are DC-AC inverters, they need to have a stable power supply to work well.
The DC side will have a fixed power supply (I mean fixed tranformation, but variable output loading), with maximums for both voltage and current. As you load an amplifier down, you are asking it to make more current, but this current has to come from somewhere, namely your vehicle. And innefficient sub with a low impedance hooked up to a huge amplifer will mean big current draw.
But how does different impedance ratings of subs compare to each other? They don't, not in any way shape or form. A 1 ohm sub is not better or worse than an 8 ohm sub. Each sub has qualities that may be better suited to each system's individual needs. Find the sub that best suits your style of music (don't buy 8" subs if you like loud hip-hop) and your amplifier (don't buy a $1000 1ohm monster for a 50 watt amplifier).
08-21-2008, 07:52 PM
#4
50 Watt CAFz'r
Join Date: Jul 2007
Posts: 84
good read macguyver,thanks. to the op,amp manufacturers ratings, for example,4 ohm stable.would you want to present that amp with a 2 ohm load? i dont believe so. thats why its rated 4 ohm stable. if its a 3 ohm sub i would go with an amp that could accept at least a 3 ohm load.
09-26-2008, 07:55 PM
#5
500 Watt CAFz'r
Join Date: Sep 2008
Posts: 723
I'm not new to having car audio equipment, but I still have no idea how it all works.
Macguyver's post helped out quite a bit. Thanks for that.
Right now I'm looking to get a new, tighter sounding, 10" sub. I am currently running an Alpine Type S in a band-pass enclosure. A very poor decision on my part, considering that 90% of the music I listen to is rock/alternative, and needs crisper bass production. I'm not sure if the subwoofer is a 2 or 4-ohm unit. When I bought it, it was already in the box.
The amp I'm currently using is a Memphis Belle 16-ST1300D. From the specs I have on this unit, it'll output 1@1120W to 1 Ohm, 1@682W to 2 Ohms, and 1@410W to 4 Ohms.
Now, if the amp is capable of sending power to a sub that produces 1 Ohm of resistance, is that easier on the amplifier than sending less power to a 4 Ohm sub? Will sound quality improve if there's less resistance from the sub on the amp?
Once I get a better grasp on how subs and amp interact, I'll choose a sub that is nice and tight.
Thanks.
Macguyver's post helped out quite a bit. Thanks for that.
Right now I'm looking to get a new, tighter sounding, 10" sub. I am currently running an Alpine Type S in a band-pass enclosure. A very poor decision on my part, considering that 90% of the music I listen to is rock/alternative, and needs crisper bass production. I'm not sure if the subwoofer is a 2 or 4-ohm unit. When I bought it, it was already in the box.
The amp I'm currently using is a Memphis Belle 16-ST1300D. From the specs I have on this unit, it'll output 1@1120W to 1 Ohm, 1@682W to 2 Ohms, and 1@410W to 4 Ohms.
Now, if the amp is capable of sending power to a sub that produces 1 Ohm of resistance, is that easier on the amplifier than sending less power to a 4 Ohm sub? Will sound quality improve if there's less resistance from the sub on the amp?
Once I get a better grasp on how subs and amp interact, I'll choose a sub that is nice and tight.
Thanks.
09-27-2008, 11:10 AM
#6
50 Watt CAFz'r
Join Date: Sep 2006
Posts: 297
As you increase the resistance you will see a higher damping factor. This will provide a marginal increase in sound quality. I say marginal because some people can't hear the difference. As you lower the resistance you make the amp work harder because it has to supply more current.
Changing the resistance of your driver will not make your system sound significantly better (tighter in your case). Tightness is something you will hear by improving the enclosure you have. Try building a proper enclosure for your sub and you will probably see an improvement in sound quality. Try building a 1 ft^3 sealed box or a 1.2 ft^3 ported box tuned to 35hz (you can use one 3" diameter port 12" in legth). By changing the enclosure you will change how the woofer behaves and might find that 'tightness' you want.
If you are dead set on replacing your subwoofer read this article from Stereo Integrity:
http://stereointegrity.com/docs/WooferSpeed.pdf
It gives a great technical explanation of how inductance can affect woofer speed.
Changing the resistance of your driver will not make your system sound significantly better (tighter in your case). Tightness is something you will hear by improving the enclosure you have. Try building a proper enclosure for your sub and you will probably see an improvement in sound quality. Try building a 1 ft^3 sealed box or a 1.2 ft^3 ported box tuned to 35hz (you can use one 3" diameter port 12" in legth). By changing the enclosure you will change how the woofer behaves and might find that 'tightness' you want.
If you are dead set on replacing your subwoofer read this article from Stereo Integrity:
http://stereointegrity.com/docs/WooferSpeed.pdf
It gives a great technical explanation of how inductance can affect woofer speed.
09-28-2008, 05:21 AM
#7
500 Watt CAFz'r
Join Date: Sep 2008
Posts: 723
If your intent is to have controlled bass, rather than excessively loud bass (subjective, I know), is a higher level of damping generally considered a good thing?
The sub I'm looking at now is the JBL P1022.
SPECIFICATIONS
General
Power Handling, RMS 400 Watts
Power Handling, Peak 1200 Watts
Sensitivity 96dB
Mounting Depth 5-7/8"
Cut-Out Diameter 9-1/16"
Impedance Dual 2 Ohms voice coils can be wired to deliver either a 1 ohm or 4 ohm load
The JBL P1024, is essentially the same woofer, except for two differences. One, it is a DVC 4 Ohm. And two, it has a sensitivity rating at 90db. This means that the P1022 (@96dB) is a more efficient subwoofer. Which, in turn, means that I should be able to get the desired volume level from the P1022 without having to amplify it as much, which is easier on the amp...
However, because the P1024 puts a 4 Ohm load on the amp there's a higher damper factor with this sub, which marginally increases the sound quality. Resistance (Ohms) is kinda like a shock absorber?
Here's the stats on the Type S I'm currently displeased with...
* Sensitivity: 84 dB
* RMS Power Range : 50-300 Watts
* Peak Power Handling: 900 Watts
* Impedance: Dual 2 Ohm
* Low Frequency response: 30 Hz
* High Frequency Response: 700 Hz
* Diameter: 10 Inch
I think I'm starting to split hairs here.
Fa-heck it. I'm getting the JBL P1022, and I'm going to love it.
I do believe this is all starting to make a little sense to me. Most newbies tend to look at the Max wattage, and become oblivious to everything else.
The sub I'm looking at now is the JBL P1022.
SPECIFICATIONS
General
Power Handling, RMS 400 Watts
Power Handling, Peak 1200 Watts
Sensitivity 96dB
Mounting Depth 5-7/8"
Cut-Out Diameter 9-1/16"
Impedance Dual 2 Ohms voice coils can be wired to deliver either a 1 ohm or 4 ohm load
The JBL P1024, is essentially the same woofer, except for two differences. One, it is a DVC 4 Ohm. And two, it has a sensitivity rating at 90db. This means that the P1022 (@96dB) is a more efficient subwoofer. Which, in turn, means that I should be able to get the desired volume level from the P1022 without having to amplify it as much, which is easier on the amp...
However, because the P1024 puts a 4 Ohm load on the amp there's a higher damper factor with this sub, which marginally increases the sound quality. Resistance (Ohms) is kinda like a shock absorber?
Here's the stats on the Type S I'm currently displeased with...
* Sensitivity: 84 dB
* RMS Power Range : 50-300 Watts
* Peak Power Handling: 900 Watts
* Impedance: Dual 2 Ohm
* Low Frequency response: 30 Hz
* High Frequency Response: 700 Hz
* Diameter: 10 Inch
I think I'm starting to split hairs here.
Fa-heck it. I'm getting the JBL P1022, and I'm going to love it.
I do believe this is all starting to make a little sense to me. Most newbies tend to look at the Max wattage, and become oblivious to everything else.
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